In many situations it is desired to be able to change the visual appearance of an object, sometimes even in a dynamical way. For example, a retailer wants to attract a customer's attention to a product to improve the sales of the product, and such attention is typically attracted by the visual appearance of the product, by using stickers, labels, posters and other promotional material. In supermarkets, placing products on the head of gondolas or in temporary displays in the main route can give a large increase in conversion. Compelling customers to go from the main path into an aisle is something a retailer pays a lot of attention to when placing products or planning promotions. For example, labels with special promotions are put on the front of the shelves, or pop-out banners or wobblers are hung from the shelf.
Also, in a home or office environment one may want to be able to change the visual appearance of for example a wall in order to create a certain atmosphere.
The visual appearance of an object can be changed, for example, by projecting an image onto the object's surface with a projection system. A drawback of this approach is that a projection system is relatively expensive and installing such a system is relatively difficult as corrections have to be made for projecting images under an angle or on a curved target surface.
The visual appearance of an object can also be changed by illumination with a light source to induce an optical response in at least a part of the object's surface. An “optical response” refers to a change of color due to the absorption of incident light. Absorption of light can for example be used to excite a photoluminescent compound, or to reversibly transform a compound between two forms having different absorption spectra. In these cases, the optical response is referred to as “photoluminescence” and “photochromism”, respectively.
In an example of photoluminescence as optical response, the surface may comprise a photoluminescent material that is applied in a certain graphical representation, so that under illumination with a suitable light source the photoluminescent material is photoexcited and starts to emit light thereby making the graphical representation visible. US-2005/0008830 discloses an article having a photoluminescent graphic disposed on an area of the article's outer cover. Upon exposure of the photoluminescent graphic to excitation light, the graphic becomes visible, for example in low-light conditions and/or after removal of the excitation light (glow-in-the-dark effect).
US-2003/0211288 discloses a plastic article wherein a photoluminescent material is incorporated into the plastic material from which the article is formed. Ambient light entering the body of the plastic article can excite the photoluminescent material, and the light that is emitted by the photoluminescent material can exit the article at locations defined by cuts and/or protrusions defining a graphic image.
For optical responses such as mentioned above, illumination with a light source may not only make a graphical representation visible, but could also change the visual appearance of any remaining part of the object's surface, and likely also of any other surface close to the object and/or in the output beam of the light source. For example, if the photoluminescent material is a phosphor that can be excited with ultraviolet light, illumination with an ultraviolet light source will also induce photoluminescence of optical whiteners in clothing of people standing close to the product and/or in the output beam of the ultraviolet light source. Furthermore, ultraviolet light sources typically also provide output in the blue part of the visible spectrum. The presence of such a visible component in the output of the ultraviolet light source will result in an undesired change of visual appearance of the illuminated object, particularly if one only wants to visualize the graphical representation defined by the photoluminescent material, without changing the appearance of any other part of the object.
It is an object of the invention to provide a solution for changing the visual appearance of at least part of an object, preferably in a dynamical way, while reducing at least some of the aforementioned drawbacks.